In apparatuses employing an electrophotographic technique such as a copying machine, a printer, and a facsimile, a two-component developer including a toner and a carrier for developing an electrostatic latent image on the surface of a photoconductive member is contained in a developing device. The developing device supplies the toner to the surface of the photoconductive member.
In a dry two-component developer, a toner is consumed by development of a latent image but a carrier remains in the developing device. A resin coat material on the surface of the carrier peels or a toner component adheres to the surface. Such a carrier lowers charging performance of the developer and causes deterioration in an image characteristic.
JP-A-9-185177 discloses a developing method for storing a developer as a mixture of a toner and a small amount of carrier in a toner cartridge and supplying the carrier to a developing device together with the toner in order to gradually replace the carrier.
However, in the developing method disclosed in JP-A-9-185177, the carrier is supplied to the developing device simultaneously with the supply of the toner. Therefore, when an image with a high printing ratio is continuously printed on a large number of sheets, the developer in the developing device increases. In particular, when a developer surface position under a developing roller rises, the developer once used for development is directly served for development again. Originally, the developer once used for development is peeled off onto a carrying mixer and agitated and carried. However, when the developer surface position under the developing roller rises, the developer used for development is dragged by the rotation of the developing roller. The rise in the developer surface position under the developing roller causes image deterioration such as density unevenness of a solid image.
Therefore, the present invention provides a developing apparatus that efficiently discharges a developer contained in a tank and suppresses an increase in a developer amount.